We've got a split king bed with adjustable platform so our bed is up and down, etc. The more expensive sheets have a wide band of elastic about 14-16 inches from the corner that goes across the corner to help the sheet stay on. But that's just corners and doesn't address the sides. If you have a mattress with some weight to it I'd suggest you do what motels and hotels do...just use flat sheets only. This way you have large amounts of sheet to tuck under and the weight of the mattress holds the sheet in place. Plus, no more struggle to fold fitted sheets!
You can buy elastic clips. Walmart sells them they keep the sheets on the corners and sides. They cost approximately $4 for 4.
Yes the clips work but if your buying sheets, get them with deep enough pockets - they now make fitted bottom sheets with varying pocket depth.... this makes them stay on better if they fully fit the mattress. Measure you mattress depth.
sheet suspenders come to fit varying mattress sizes.... https://www.amazon.com/s?k=sheet+suspenders&crid=TJLDPG0UCCL5&sprefix=sheet+susp%2Caps%2C224&ref=nb_sb_ss_i_1_10
If you look at the fitted sheets you will see what I mean about pocket depth.... https://www.amazon.com/s?k=bottom+fitted+sheet+queen&crid=8LX6T8E2KZ84&sprefix=bottom+fitted+%2Caps%2C225&ref=nb_sb_ss_i_1_14
They have something at walmart in the sheets department that clip no the sheets to hold the. In place
Go to walmart in the department where the sheets are clip go on them will hold the sheets to hold in place